This invention relates to silver complex diffusion transfer materials and more particularly to negative materials which are to be subjected to silver complex diffusion transfer development in combination with positive materials.
In silver complex diffusion transfer processes, there are generally used a negative material comprising a support and silver halide emulsion layers coated thereon, a positive material comprising a support and an image receiving layer containing physical development nuclei coated thereon and a processing solution containing a silver halide solvent. That is, exposed silver halide of exposed negative material is developed (chemically) with developing agent in the processing solution or in the negative material and simultaneously silver halide of unexposed area reacts with the silver halide solvent in the processing solution to form a soluble silver complex which diffuses to the positive material (image receiving material) where it precipitates on physical development nuclei to form silver images.
Qualities of final images such as density, color tone, contrast, storage stability, etc. are important in such silver complex diffusion transfer process. Depending on uses, a continuous tone original is reproduced on the image receiving material and the higher contrast, sharpness and resolving power are required for using it as reproduction of documents, printed matters, etc. or as block copies for printing plate making. Furthermore, the recent silver complex diffusion transfer development which is designed to obtain higher transfer efficiency, namely, to complete the transfer in 5-15 seconds necessitates obtaining sufficient transfer density in a short time.
Silver complex forming agents necessary for dissolving unexposed, namely, undeveloped silver halide, especially sodium thiosulfate are usually incorporated in the processing solution or image receiving materials. Therefore, the positive material on which an image has been formed contains at least some sodium thiosulfate, which decreases concentration of silver ion to cause increase of oxidation potential of metallic silver. As a result, the silver image is oxidized and becomes liable to conversion to a double salt or a simple silver salt. This brings about disappearance of the silver image or change in color of the image to brown especially in an atmosphere of high humidity.
The silver image of such portion where only a small amount of silver is precipitated due to the short transfer time is especially liable to disappear. This defect is accelerated in the case of the closed system where both the negative and positive materials have water impermeable supports and diffusion of the processing solution is restrained.
For obtaining further higher sharpness and resolving power, it is well known to allow carbon black, pigments, dyes, etc. to be present in silver halide photographic materials. However, when these substances are contained in silver halide emulsion layers, loss of sensitivity is too much and so they are preferably present in the layers other than the silver halide emulsion layer.